Priceline.com review: Travel credits

In Oct 2022 I booked a trip with my husband, two kids and my Mom and Dad to celebrate my Mom’s 60th and my 40th birthday. The trip was planned for March 2023. In Jan 2023 my Mom was diagnosed with cancer. I called Priceline and was told we would have until Oct 2023 to rebook the tickets. I found flights well within our credit price, called to rebook and and was told they could do it but for an additional $1000. When I asked why there was a cost difference I got no explanation. I asked toto speak with a supervisor. She told me someone would call in 3 business days. That was on August 2nd. I spent 2 1/2 hours on the phone with them that day. Never received a call back. I called Sept 21st to try again to rebook- was passed to 3 different people. Told it was being escalated to upper management and I would receive a call back in 24-48 hours. It’s been a week and still no call. That was another 2 hours spend on the phone. Our 6 ticket credit is $3000 - I have the email that clearly says I have travel credits. United shows my travel credits but yet I have to rebook through Priceline. How do so resolve this when I can’t get someone to actually help me - they are stealing $3000!